Pattern of omission bias across various measures of moral judgement: Insights from the use of Young et al. (2007) vignettes.

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People are more forgiving towards harmful inaction (omission) over harmful action (commission), even when the eventual outcome is identical-known as omission bias. This phenomenon is observed in a set of moral vignettes by Young et al. that was originally designed to investigate moral judgement based on the presence of harmful intent and outcome. However, studies that used this set of vignettes have never reported the "action/omission" distinction effect, thus overlooking or conflating the impact of omission bias and potentially complicating the understanding of the targeted moral construct. In this report, we demonstrate how this omission bias may have inadvertently been incorporated into Young et al. vignettes. We analysed data from two published studies by separating the values of each moral measure into action and omission, and included them as an additional two-level factor into the model used in each included study. Overall, our results revealed statistically significant effect of omission bias. Interestingly, this effect was observed only in explicit but not implicit measures (i.e., implicit association test (IAT)), though both measures were able to capture their intended effect of "intent-outcome"-based moral reasoning. Furthermore, this report offers preliminary insights into how the action-omission asymmetry relates to intent-outcome-based moral reasoning across various categories of moral judgement, suggesting avenues for future exploration.